Switch to the new way to upload coverage (using the PYPI packages was deprecated)

.github/workflows/main.yml

@@ -23,12 +23,14 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install -U setuptools
-        pip install tox tox-gh-actions codecov
+        pip install tox tox-gh-actions
     - name: Type checking
       continue-on-error: true
       run: |
         tox -e mypy
     - name: Test with tox
-      run: |
-        tox
-        codecov
+      run: tox
+    - uses: codecov/codecov-action@v3
+      with:
+        fail_ci_if_error: true
+        verbose: true # optional (default = false)